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The spatial distributions of marine fish populations are influenced by environmental conditions, intrinsic properties of the populations, and prior distribution. The influence of these factors may not be consistent across age classes. For this study, age composition estimates for walleye pollock (Gadus chalcogrammus) collected on bottom-trawl surveys in the Bering Sea were used to estimate range correlation indices, population centers of gravity, and effective area occupied. Age-specific density maps suggested a circular ontogenic migration during the summer feeding season, with the youngest and oldest groups most broadly distributed. Range correlation analysis among age groups and year classes provided clear evidence of a population cohort effect in the spatial distribution of the population. Variance decomposition analysis indicated that the variance in the spatial distribution of age groups during summer was influenced by the initial distribution of that cohort as recruits. Model-based analyses showed that extrinsic temperature variables affected the youngest and oldest age classes the most, but provided no indication of age-related effects for intrinsic population factors. This study showed that both cohort and age-specific factors are important drivers of spatial distribution. [ABSTRACT FROM AUTHOR]

Skates are a diverse group of dorso-ventrally compressed cartilaginous fish found primarily in high-latitude seas. These slow-growing oviparous fish deposit their fertilized eggs into cases, which then rest on the seafloor. Developing skates remain in their cases for 1–4 years after they are deposited, meaning the abiotic characteristics of the deposition sites, such as current and substrate type, must interact with the capsule in a way to promote long residency. Egg cases are morphologically variable and can be identified to species. Both the gross morphology and the microstructures of the egg case interact with substrate to determine how well a case stays in place on a current-swept seafloor. Our study investigated the egg case hydrodynamics of eight North Pacific skate species to understand how their morphology affects their ability to stay in place. We used a flume to measure maximum current velocity, or "break-away velocity," each egg case could withstand before being swept off the substrate and a tilt table to measure the coefficient of static friction between each case and the substrate. We also used the programing software R to calculate theoretical drag on the egg cases of each species. For all flume trials, we found the morphology of egg cases and their orientation to flow to be significantly correlated with break-away velocity. In certain species, the morphology of the egg case was correlated with flow rate required to dislodge a case from the substrate in addition to the drag experienced in both the theoretical and flume experiments. These results effectively measure how well the egg cases of different species remain stationary in a similar habitat. Parsing out attachment biases and discrepancies in flow regimes of egg cases allows us to identify where we are likely to find other elusive species nursery sites. These results will aid predictive models for locating new nursery habitats and protective policies for avoiding the destruction of these nursery sites. [ABSTRACT FROM AUTHOR]

The population structure and demographic history of a pelagic lumpsucker, Aptocyclus ventricosus, were investigated on the basis of sequence variation in the mitochondrial cytochrome b gene (1038 bp). The haplotype network clearly recovered two haplotype groups, consisting of western and eastern North Pacific individuals, except for some specimens collected from offshore of Tohoku, northern Japan. The geographic distribution of haplotypes suggests that the ocean currents in the North Pacific have shaped the population structure of the species after historical vicariant events between the Kuril Islands and Kamchatka Peninsula. In addition, the demographic histories of the two haplotype groups were quite different, suggesting that the western North Pacific group experienced a population expansion starting around 10,000 years ago, while the population size of the eastern North Pacific group has remained more stable. [ABSTRACT FROM AUTHOR]

Poleward species range shifts have been predicted to result from climate change, and many observations have confirmed such movement. Poleward shifts may represent a homogeneous shift in distribution, seasonal northward movement of specific populations, or colonization processes at the poleward edge of the distribution. The ecosystem of the Bering Sea has been changing along with the climate, moving from an arctic to a subarctic system. Several fish species have been observed farther north than previously reported and in increasing abundances. We examined one of these fish species, Pacific cod, in the northern Bering Sea (NBS) to assess whether they migrated from another stock in the eastern Bering Sea (EBS), Gulf of Alaska, or Aleutian Islands, or whether they represent a separate population. Genetic analyses using 3,599 single nucleotide polymorphism markers indicated that nonspawning cod collected in August 2017 in the NBS were similar to spawning stocks of cod in the EBS. This result suggests escalating northward movement of the large EBS stock during summer months. Whether the cod observed in the NBS migrate south during winter to spawn or remain in the NBS as a sink population is unknown. [ABSTRACT FROM AUTHOR]

The zoarcoid family Bathymasteridae contains seven species in three genera (Bathymaster, Rathbunella, Ronquilus) found in the North Pacific Ocean. Although several synapomorphies have been identified for the family, molecular analyses recover the family as a paraphyletic grade. The goals of this study are to provide a description of the skeleton of R. jordani as a baseline contribution for future systematic comparisons among all bathymasterid taxa and zoarcoids. We used our osteological study to discuss ontogenetically variable characters that appear to carry phylogenetic signal within Zoarcoidei. Finally, we discuss the systematic relationships of Bathymasteridae, including its monophyly and their systematic relationships. The vertebrae of Bathymasteridae develop in two distinct patterns. In Ronquilus and Bathymaster, the vertebrae initially form in the mid‐caudal region and development proceeds both anteriorly and posteriorly until the entire vertebral column is complete. In contrast, in Rathbunella the vertebrae initially form immediately posterior to the skull and development proceeds posteriorly; this is interpreted to be plesiomorphic. Other characters that were clarified (e.g., presence of well‐developed teeth on the gill rakers of Ronquilus) or described (e.g., variation in fusion caudal skeleton elements across Zoarcoidei) now must be evaluated in a taxonomically comprehensive systematic analysis of Zoarcoidei. [ABSTRACT FROM AUTHOR]

From late 2014 through 2017, fishery observers in the North Pacific Observer Program, National Marine Fisheries Service, were trained in the identification and sampling of skate egg cases to investigate the interactions between fisheries and skate nursery areas in the eastern Bering Sea. Trained observers identified and assessed 2887 egg cases in a wide range of fisheries across all gear types, with the majority of egg cases being encountered on vessels targeting deepwater species, such as the arrowtooth flounder (Atheresthes stomias), Greenland halibut (Reinhardtius hippoglossoides), Pacific cod (Gadus macrocephalus), and sablefish (Anoplopoma fimbria). A large proportion of the egg cases identified were reported on boats using bottom trawling gear, but an even greater proportion were reported on longliners. Egg cases identified represent 10 skate taxa. Over half (67%) of them were identified as Alaska skate (Bathyraja parmifera), and 19% were identified as either Aleutian skate (B. aleutica) or Bering skate (B. interrupta). More than 42% of all the egg cases assessed were viable (contained a living skate); over 50% of egg cases of Alaska skate and of egg cases encountered on longliners were viable. The highest concentrations of egg cases generally were reported near known skate nursery areas, particularly in the Bering, Pribilof, and Pervenets Canyons. [ABSTRACT FROM AUTHOR]

Species composition data collected by observers in the North Pacific Observer Program are critical to the effective management of Alaska’s commercial fisheries. However, there has been no attempt to quantify the reliability of observer species identifications. Digital cameras were issued to over 120 groundfish observers, who were instructed to document via digital photographs a pre-selected series of fish identifications and submit the photos for analysis at the end of their deployments. Identifications represented by the photos were then assessed visually by the author for identification accuracy. Over 3000 individual identifications were documented, and over 99% of those identifications were correct. Identification accuracy rates for each of the commercial species groups identified by observers (flatfishes, cods, rockfishes, and salmon) were over 98%. Accuracy rates for some non-target species groups, such as sculpins and smelts, were slightly lower. Identifications documented for this study represent a broad spectrum of target fisheries, gear types, and observer experience levels, and therefore are likely to be a reasonable representation of observer identification accuracy throughout the Observer Program. Although there are potential sources of bias that may have inflated these accuracy rates, this study suggests that the overall reliability of species identifications in the North Pacific Observer Program is quite high. [ABSTRACT FROM AUTHOR]

Six years of bottom-trawl survey data, including over 6000 trawls covering over 200 km² of bottom area throughout Alaska's subarctic marine waters, were analyzed for patterns in species richness, diversity, density, and distribution of skates. The Bering Sea continental shelf and slope, Aleutian Islands, and Gulf of Alaska regions were stratified by geographic subregion and depth. Species richness and relative density of skates increased with depth to the shelf break in all regions. The Bering Sea shelf was dominated by the Alaska skate (Bathyraja parmifera), but species richness and diversity were low. On the Bering Sea slope, richness and diversity were higher in the shallow stratum, and relative density appeared higher in subregions dominated by canyons. In the Aleutian Islands and Gulf of Alaska, species richness and relative density were generally highest in the deepest depth strata. The data and distribution maps presented here are based on species-level data collected throughout the marine waters of Alaska, and this article represents the most comprehensive summary of the skate fauna of the region published to date. [ABSTRACT FROM AUTHOR]